1
Paper #09 11- 10 – 2009
A Comparison of Heterogeneous Video Multicast schemes: Layered encoding or Stream Replication
Authors: Taehyun Kim and Mostafa H. Ammar
Presented by:Koushik AnanthasayanamVarun Kulkarni
2
Overview ~Aim of the research paper
Comparison between Replication and Layering
Experiments based on the Comparisons
Results
Conclusion
3
What this paper aims at ?A structured and systematic comparison of
video multicasting schemes.
Only those schemes that deal with the heterogeneous receivers.
Replicated Streams.
Cumulative layering.
Non- cumulative Layering.
4
Aim (Contd.)‘Layered multicast transmission
is superior to the replicated stream multicasting’ – widely believed.
Authors contradict this dogma – bandwidth overhead which is incurred by encoding video stream in layers, cannot be neglected while comparison.
5
Replicated Streams ~More than one video streams.
Replicated – same contents but with different data rates.
However, receiver subscribes to only one suitable stream.
Examples: SureStream by RealNetworks.Intelligent Streaming by Microsoft.
6
Replicated Streams (Contd.)
7
Replicated Streams (Contd.)R1, R2 and R3 are from different domain
Receivers subscribe to only one stream
R1 joins the high quality stream (8.5Mbps)
R2 receives the medium quality stream (1.37Mbps)
R3 joins the low quality stream (128kbps)
8
Cumulative Layering ~Video can encoded in a base layer and one
or more enhancement layers.
Base Layer: Independently decoded.
Enhancement Layer(s): Decoded with lower layers to improve the video quality.Layer ‘k’ can be only be decoded along with layers 1 to k-1.
Example: MPEG-2 scalability modes.
9
Non- Cumulative Layering ~Video is encoded in two or more
independent layers.Two or more independently
decoded layers.Receivers select any subset of
video layer and join it, without joining the layer-1 multicast group.
Eg: Multiple Description Coding.
10
Layered Multicast (Contd.)
11
Layered Multicast (Contd.)R1 subscribes to all video layers
(10 Mbps)
R2 joins enhancement layers 1 and the base layer (1.5 Mbps)
R3 just receives the base layer (128kbps)
12
Layering or Replication ?Common belief: ‘Layering is better
than replication.’ - Really ?
Bandwidth overhead in layering.
Cater to specifics of encoding.
Implicit Protocol Complexity
Topological placement of receivers
13
Layering or Replication ? (Contd.)
14
Layering or Replication (Contd.)Assuming 20% overhead, the
data rates contributing to the video quality are 8Mbps, 1.2Mbps and 102.4Kbps
Stream Replication: video quality are 8.5Mbps, 1.37Mbps and 128kbps
15
Overhead in Layered Video ~Information theoretic results: Performance of layered coding is not better than that
of non-layered coding. Increase the number of layers - significant quality degradation.
Packetization Overhead: Enhancement layers carry: Picture header, GoP
information and Macroblock information.
Protocol Overhead: Receivers need to manage the multiple subscriptions
in layered video.
16
Experimental Evidence ~Non-layered streams
has better video quality
The layering overhead ranges from 0.4% at 27.7dB PSNR to 117% at 23.2dB PSNR
For a good quality video, the overhead is around 20%
17
A Fair Comparison ~ In order to have a meaningful comparison, need
to ensure that each scheme is optimal.
Stream Assignment Algorithm: Determine the reception rate of each receiver by aggregating the data rates of the assigned streams
Rate Allocation Algorithm: Determine the data rate of each stream.
Goal: Maximize the bandwidth utilization by each scheme for a given network, a particular set of receivers and given available bandwidth on the network links
18
System ModelModel the network by a graph G = (V, E) V is
a set of routers and hosts E is a set of edges representing connection links.
n is number of receivers
Isolated rate:The reception rate of the receiver if there is no constraint from other receivers in the same session
19
Stream AssignmentCumulative Layering: Given stream
rates αi
- Assign as many layers as possible: Compute the isolated ratesAssign Σi αi that does not exceed the isolated
rate.
20
Stream Assignment (Contd.)
Stream replication◦ Define δ = {δi | δi ε R+, i =1,…,m}
δi is the data rate of a replicated stream and m is the number of replicated streams
Set of receivers assigned to stream i.◦ Two objectives
Minimum reception rate for all receivers is greater than zero
Maximum as much as possible.
Greedy algorithm◦ Allocate δ1 to all receivers to satisfy the minimum
reception rate constraint◦ Receiver is assigned a stream that has not been
assigned and has the maximum value of group size and stream rate product
◦ Receiver can either subscribe to base or any other high quality layer.
21
Stream Assignment (Contd.)Non-cumulative layering
◦ Define i is the data rate of a non-cumulatively
layered stream and m is the number of streams
Set of receivers assigned to stream i
◦ Two objectives Minimum reception rate for all receivers
is greater than zero Maximum as much as possible.
miRii ,...,1,|
22
Stream Assignment Algorithm for Replicated Stream Multicasting
• A receiver can subscribe to either the base layer stream or high quality stream
23
Stream Assignment Algorithm for Non-cumulatively layered multicasting
• A Receiver can subscribe to multiple streams. The data rate of the aggregated streams leads to the minimum distortion.
24
Rate AllocationCumulative layering
◦ Optimal receiver partitioning algorithm determines the optimal rates of layer i, i Receivers are partitioned into K groups (G1, G2,
…, GK) Objective is to maximize the sum of receiver
utilities Dynamic programming algorithm is used to find
an optimal partition For a given partition, an optimal group
transmission rate can be determinedStream replication
◦ Stream rates, i, are allocated based on the optimal cumulative layering rate.
◦ 1 is the stream rate of the base. If a receiver can join up to k layers, the receiver has the capability to join a replicated stream of data rate k.
25
Rate Allocation (Contd.)Non-cumulative layering
◦ Receiver can subscribe to any subset of layers without joining the base layer
◦ = data rate of non-cumulatively layered stream.
◦ Given non-cumulative layered stream ={1,2,4} => selective subscription: isolated rates of {1,2,3,4,5,6,7}
◦ 2m-1 different link capacities with m non-cumulative layers
◦ i are allocated based on i =>
43213
32121
212
11
26
Experiments ( Performance
Metrics)~Average reception rate
◦ Average rate received by a receiver
Average effective reception rate◦ Amount of data received less the layering overhead
Total bandwidth usage◦ Adding the total traffic carried by all links in the
network for the multicast session
Efficiency◦ total effective reception rate / total bandwidth usage
27
Network ModelGeorgia Tech Internetwork Topology Models
(GT-ITM)◦ 1 server◦ 1640 nodes with 10 transit domains◦ 4 nodes per transit domains, 4 stubs per
transit node, 10 nodes in a stub domain◦ transit-to-transit edges = 2.4Gbps ◦ stub-to-stub edges = 10Mbps and 1.5Mbps ◦ transit-to-stub edges = 155Mbps, 45Mbps
and 1.5Mbps ◦ number of layers = 8◦ amount of penalty = 20%
28
Experiment ResultsRandom Receiver Distribution - Reception
Rate: Cumulative
layering can receive more data
Number of layers in cumulative layering is twice as many as that of non-cumulative layering
29
Experiment Results Random Receiver Distribution - Effective Reception Rate:
Stream replication has the highest effective reception rate.
30
Experiment ResultsRandom Receiver Distribution - Total Bandwidth usage:
Cumulative layering has the highest Total Bandwidth Usage.
31
Experiment Results Random Receiver Distribution - Bandwidth usage efficiency:
Stream Replication has the highest Bandwidth usage Efficiency.
32
Experiment Results Clustered receiver distribution.
33
Protocol ComplexityReceiver-driven Layered Multicast (RLM)
Receivers decide whether to drop additional layer or not Join experiment incur a bandwidth overhead Receivers send a join message and multicast a message
identifying the experimental layer to the group
Layered video multicasting◦ Receiver can join multiple groups◦ Large multicast group size
Replicated stream video multicasting◦ Receiver only join one group◦ Small multicast group size
34
Experimental ResultsAverage number of groups and average
groups size.
35
Experiment ResultsThe receivers are randomly
distributed.
The group size in cumulatively layered video multicasting is twice as large as that in stream replication.
Layered multicasting requires more bandwidth.
36
Experiment Results (Contd.)Receiver in a cumulatively layered
video multicast session requires more buffer size and better synchronization capability than replicated stream video multicasting
Receiver in cumulative layering subscribes to more than five layers on average whereas a receiver in stream replication subscribes to only one stream
37
Conclusion The Paper has identified the factors affecting relative
merits of layering versus replication◦ Layering penalty◦ Specifics of the encoding◦ Protocol complexity◦ Topological placement
It has developed stream assignment and rate allocation algorithms
And Investigated the conditions under which each scheme is superior
Paper has given a new comparison approach towards video multicast streams
38
Our Comments!The paper brings up an unbiased support for
stream replication approach.
The people supporting only Layered stream multicast approach should re- think.
The paper concludes the support for stream replicating approach based on specific scenarios.
More generalization in experimental scenarios is essential to strengthen the specified support.
39
Questions ??
